Excerpts from countryliving.com:

Each week, Chicago Fire delivers enough emotional twists and turns to make our heads spin. The show has been known to shock audiences with painful deaths and teary-eyed breakups but, as its name would suggest, it also showcases plenty of fires.

The members of the Firehouse 51 team have rescued countless pedestrians, responded to devastating car crashes, and ran into burning buildings. The high-stakes scenarios and the actors’s professionalism make it easy to forget that they’re not actually firefighters. Still, the cast of Chicago Fire isn’t just reading lines when the cameras start rolling—they’re acting based off of training they’ve done with the Chicago Fire Department.

The cast is put through training that mimics real-life scenarios faced by firefighters. The actors have worn all of the gear, knocked down doors, used the Jaws of Life to break into cars, and walked through rooms so filled with smoke that it’s impossible to see.

The idea behind these exercises is that each experience gives the cast a better idea of what being a firefighter is really like, so they can portray that to audiences. Based on the emotional reactions from fans after every episode, it’s safe to say they’re doing a good job.

thanks Martin